1. Field of the Invention
The present invention relates to parachute release mechanisms for releasing a deployed parachute from a suspended load in a controlled manner.
2. Description of the Prior Art
Aerial delivery is a means frequently used for transporting cargo quickly to areas of limited or hostile access, without the availability of any nearby airports. At times, people in isolated areas, such as jungles, deserts, mountains, polar regions, or combat zones, are in need of essential supplies, including food and medical supplies, but are not within access to an airport at which a supply plane could land. In these instances, aerial delivery of cargo from in-flight aircraft is the sole option. These aerial delivery systems involve the use of parachute systems to slow the descent and gently land the cargo platforms on the ground.
Similar parachute systems are further utilized for recovery of aeronautical and astronautical vehicles, including rocket boosters, experimental aircraft and space capsules, returning back to the earth's surface from flights in the upper atmosphere or outer space.
In these aerial delivery or recovery systems, a series of parachute deployments is often used to progressively slow the decent velocity of the payload. Use of a series of parachute deployments is often necessary because the force and impulse on the suspension lines and straps of a main parachute (i.e., one large enough to slow the cargo platform to an acceptable landing velocity) deploying at the terminal, free-fall velocity of the cargo platform would be excessive, causing the parachute system to fail. Instead, the cargo platform is typically slowed in a series of stages using subsequently larger parachutes.
A drogue parachute is typically deployed first from the parachute system. The drogue is a small parachute which can be easily deployed from its container by a tether attached to the launching cargo plane or by an easily deployed stored energy means such as a spring launched pilot parachute. As the drogue parachute is deployed and inflated, it moderately decelerates the suspended cargo platform, without excessive strain on the slings and parachute canopy from which the cargo platform is suspended. After a pre-determined time period, the drogue parachute is released from the suspended cargo platform. The drag provided by the released drogue parachute is then utilized to pull and deploy the next, larger parachute. This next parachute may be the final, main parachute, or another intermediary parachute prior to another subsequent deployment of the main parachute, depending upon the size of the cargo platform and the design of the parachute system.
To accomplish this release design, the drogue parachute is attached to the suspended cargo platform by a release mechanism. The suspended cargo platform is suspended from the release mechanism typically by a series of suspension slings. The suspension slings maintain the suspended cargo platform in a stable, level attitude. The number of suspension slings is typically four, with one routed to each corner of a square or rectangular cargo platform supporting the suspended cargo. For larger platforms, a greater number of suspension slings may be used. The suspension slings converge at a point above the suspended load to the release mechanism, located at the apex of the pyramid formed by the suspension slings.
The release mechanism must release all attached suspension slings simultaneously, otherwise the suspended cargo platform will pitch or roll after release, jeopardizing successful deployment of the next parachute. Various means are available in the art for simultaneously releasing the suspension slings.
One such mechanism is a pyrotechnic cord cutter powered by an explosive or pyrotechnic charge. This mechanism utilizes the detonation of a small explosive charge to drive a cutting blade through the suspension sling. For example, Norton, U.S. Pat. No. 4,493,240, disclosed a pyrotechnic cord cutter comprising an elongated cylindrical body with a lateral aperture proximate to one end of the body, through which passes the suspension line or other support line in the parachute system. A chamber is located at the other end of the body, containing an explosive charge. An opening is provided in the medial end of the chamber, into which is registered the rear end of a cutting blade. Upon detonation of the explosive charge in the chamber, the cutting blade is propelled through the aperture, severing the cord within.
The release mechanisms may be configured in either a single-point or multi-point suspension release system. Either of these release systems involve a suspension system utilizing a number of suspension slings, typically four, in which the lower end of each suspension sling attaches to one corner of the load platform and the upper ends of all four suspension slings are joined by a union, forming a pyramid with an apex at the union, to which is attached the drogue parachute. In the single-point system, the release mechanism is located on a link or union at the pyramid apex which conjoins the upper ends of the suspension slings and which also conjoins with the suspension lines of the drogue parachute. Severing the link with a pyrotechnic cutter releases the upper ends of all four suspension slings simultaneously.
The single-point system is suitable for relatively light cargo platforms. As the size and weight of the suspended cargo platform increases, so to does the size and thickness of the link or union between the suspension slings and the drogue parachute suspension lines, and thus, so to does the size of the pyrotechnic charge necessary to sever the link. These larger pyrotechnic charges pose a substantial hazard to the personnel preparing the cargo delivery system and to the aircraft carrying the cargo platform to the delivery site. Larger platforms instead use a multi-point release system.
In the multi-point release system, a separate release mechanism is located on each suspension sling, typically at the lower end of each sling or on the hardware attaching the sling to the cargo platform. Thus, each pyrotechnic charge is one-fourth or smaller of the size necessary for a single-point system.
As previously noted, simultaneous release of the suspension slings is critical to assure the cargo load platform remains level during deployment of the main parachute. The single-point system only has one release mechanism which assures release of all suspension slings simultaneously. Having only one release mechanism, the single-point system is also less expensive and easier to control. However, one disadvantage is that the suspension slings, once released, remain with the cargo load platform, streaming in the air vertically above the platform, where they can potentially interfere with deployment of, and entangle with, the main parachute. Another disadvantage is that the single-point release mechanism must support the entire weight of the suspended cargo load platform, which requires a larger mechanism than those used in the multi-point systems and a larger, more hazardous, pyrotechnic charge, as previously noted.
The multi-point system, on the other hand, utilizes smaller release mechanisms, which, when based on a pyrotechnic charge, as is most commonly the case, are safer for personnel preparing and handling the parachute system. Also, upon release, the suspension slings remain with the drogue parachute rather than with the cargo load platform, eliminating the entanglement hazard of undulating suspension straps to the deploying main parachute. However, multiple release mechanisms are used, in which all the pyrotechnic charges must be detonated simultaneously for an even, controlled release of the suspended load. Almost any variation or delay in these detonations of the pyrotechnic charge could apply an asymmetrical torque to the suspended load, causing it to roll after release and interfere with subsequent deployment of the main parachute.